master: remove weaken on storable::read

6d62e6b0782ecfa0f4e0c2bec14434d675734962 introduced a weaken_config() sub, used
in munin_readconfig_storable().  It should not be needed, and some profiling
showed that it is a *huge* cpu eater.
master: remove auto_weaken()

Every weaken() should be done on construction time. Fixing it afterwards is
wrong, and might be dangerous. Let bug leaks happen and be fixed !
contrib: add a test for memory leaks
contrib: complete test with Storable dump/load

Test if Storable also saves the "weak" state.

Hint: it does.
Use a more efficient sort on the list of nodes

 - Cache the subroutine results, to improve speed when comparing.  More
   noticeable on a large number of nodes.
plugins: add doc about conntrack

As ilf noticed, then fw_conntrack plugin depends on the netfilter conntrack
userspace tools.

Updating the documentation as he suggested.

Closes: #1267
plugin/diskstats: fix negative stats, relax limits
plugins: use $PATH for external commands in shell
plugins/http_loadtime: more wget/time fixes

In autoconf $wget_bin is undefined, use wget as elsewhere. Also direct
stdout to null to make it work.

When running with bash "time" is internal bash command and it's output
can't be redirected. Force plugin to use external /usr/bin/time command
so that redirect works.
plugins/lpstat: fix autodetection

"lpstat -r" outputs data even if no printers are configured, resulting
lpstat plugin to print errors when run. Use "lpstat -v" to detect
if there really are some printers.
plugins/snmp__if_multi: prefer ifAlias for alias name

Also fix if snmpinfoX/ifHCInOctets is undefined.
plugins/postfix_mailstats: support proxy-rejected (amavis) log lines
asyncd: add more signal handlers.

The following signal handlers are added :

  * HUP enables "ssh -t node service munin-asyncd restart".
    Without it only "ssh node" works, but not with -t.

  * INT+TERM handlers are needed to kill asyncd nicely
    in init.d scripts.
plugins/postfix_mailstats: using a per-minute graph

For most setups, the volume of emails is not very high. So a
per-minute rate is much more interesting.
plugins/snmp_if: replace 32b counters by 64b ones

When 64b are present, we do not use the 32b ones, at all. Otherwise
the computation might be wrong is corner cases.
Merge branch 'bbbs' into stable-2.0
Merge branch 'perf-cgi' into stable-2.0